1. field of the Invention
This invention relates to a disk reclaimer. More particularly, the invention pertains to a disk reclaimer having modified teeth for improved blending and moving of cohesive bulk materials.
2. Discussion of the prior Art
In certain types of industrial operations involving the handling and processing of large quantities of bulk material, undesirable variations in the composition of the material can arise. For instance, the assay of ore specimens usually changes over the course of mining the ore deposits. As a consequence, when the ore is stacked, the resulting ore pile will not be entirely homogeneous. Such fluctuations in ore make-up can lead to inconsistent performance of the smelter furnace, even to decreased output. Accordingly, the ore is preferably subjected to some form of mixing treatment to render it more uniform in composition prior to use.
One technique for the blending and moving of large quantities of bulk materials make use of the disk reclaimer in a commercial process commonly referred to as reclaiming. Stated briefly, a disk reclaimer consists essentially of a spoked wheel of large diameter up to about 30 meters and having attached perpendicularly to the spokes, in a comb-like arrangement, a series of rod-like teeth.
The disk reclaimer is rotatably suspended from a horizontal supporting beam by means of a bearing located on the underside of the beam. The side of the disk containing the projecting teeth faces downward. Means are provided for turning the beam on its horizontal axis thereby allowing for the disk to be tilted. Linear travel of the entire assembly is provided by bogies on which rest the ends of the supporting beam.
The bulk material to be reclaimed is stacked in a continuous longitudinal pile situated within a trench. Along the sides of the trench are parallel tracks which engage the bogie under carriage of the supporting beam thereby enabling the disk and its supporting structure to traverse the length of the trench.
The reclaiming operation begins by advancing the disk assembly along the tracks until the disk reclaimer contacts the end of the pile, and the teeth on the spokes penetrate into the pile material. At the same time, the disk is set to rotating, the peripheral speed being generally about 1 meter per second. The tilt angle of the disk depends on pile height and the angle of repose of the bulk material.
In effecting disk reclaiming, three functional elements of the disk come into play. These elements comprise the harrow teeth, the carrier teeth and the rim. The harrow teeth occupy the inner circular regions of the disk which takes up most of the total disk area. The harrow region comprises the spokes and horizontal cross members connecting the outer ends of the spokes. Viewed from above, the harrow area of the disk resembles a polygon the periphery or perimeter of which is defined by the horizontal cross members constituting the sides of the polygon. Between the periphery of the harrow region and the disk circumference is the circular carrier area, generally about two feet in width, in which the carrier teeth are located. The disk circumference is surrounded by a flat wall-like rim.
The reclaiming process involves interaction of these functional elements. As the reclaimer disk rotates, the harrow teeth in the large inner area of the disk, agitate the pile face causing material to flow down to the outer circular band containing the carrier teeth. These teeth perform a similar digging function to that of the harrow teeth. In addition, the carrier teeth blend the material and carry it forwards and upwards by the raking action of the teeth to a side wall from where the material falls onto an outgoing conveyor belt and is transported to hopper or mill.
The harrow teeth are spaced far enough apart so as not to impede the movement of the loosened material as it tumbles down the pile face toward the outer carrier region. The carrier teeth, on the other hand, are spaced sufficiently close whereby material builds up ahead of the teeth as it is carried forward by the rotating disk.
As the reclaiming proceeds, a fresh pile of material is stacked in the trench. On reaching the end of the first pile, the disk is swung around on its horizontal axis into position against the new pile, this time rotating in the opposite direction.
Bulk materials generally fall within two categories commonly referred to as granular and cohesive.
Granular bulk materials are characterized by the presence of particles which do not deform nor bond together after compaction. Granular materials are not normally sticky and do not tend to cling to objects they come in contact with. Examples of granular bulk materials include sand, gravel, crushed stone, coal, etc.
A cohesive bulk material, with which the present invention is concerned, is one which can be tightly compacted resulting in high bulk density which remains unchanged even after removal of the compactive force. Cohesive materials contain many very fine, deformable particles, often clays, which cling together and to anything else they come into contact with.
When cohesive material freezes, especially after compaction, it forms a much more solid mass than a granular material. The cohesive material, with its finer particle size and particle deformation has a much greater particle contact area than granular material.
Phosphate shale, used in the production of phosphorus, is an example of a moist cohesive material having a high clay content. It also contains various amounts of rocks. As the shale is placed in the stockpile, the rocks roll to the bottom of the sides. As a consequence, of its own weight, the pile is compacted. During cold weather, the upper, exposed side and sloped faces of the pile freeze to a depth of up to 30 inches.
Although disk reclaiming is effective for blending of granular bulk materials, when the technique is applied to cohesive bulk materials, various problems are encountered. The basic cause of these problems can be attributed to the rigid mounting system of attaching the teeth to the spokes in presently designed disks.
In the case of the harrow section of the disk, the rigidly mounted racks of harrow teeth perform satisfactorily provided the pile material does not offer undue resistance to the movement of the teeth. For instance, when reclaiming phosphate shale in freezing temperatures, the slow forward motion of the reclaimer allows it to cut very thin layers of shale from the face of the frozen crust. The harrow racks can withstand the forces arising from this normal operation. However, contact of the harrow teeth with rocks embedded in the compacted pile face or frozen crust can generate resistive forces of sufficient magnitude to cause breakage of the harrow racks, their mounts or even the spokes of the disk.
In the case of the carrier section, problems associated with rigid mounting of the teeth are more numerous and complex than in the harrow region.
These problems can be described as follows:
1. Rocks and foreign matrix of transported material often catch between the carrying teeth and the face of the pile. Rocks in a cohesive bulk material create unique problems versus those which would be experienced in a granular material. In a granular material, rocks can displace material in the pile face ahead of the carrying teeth as they are transported in the bulk of carried material. In a cohesive shale, these same rocks cannot sufficiently compress or displace material in the already compacted pile face, so high forces are transmitted to the teeth, causing them to either bend or break.
2. In the original design, carrier teeth of triangular steel tubing were welded to a mounting tube in groups of five. Hard, wear resistant tips were epoxy glued into the end of each tooth. When tips were glued in place, the glue had to set for 24 hours before the tooth could be used. Field replacement of individual carrier teeth or tips was not possible. Whenever a tooth or tip needed work, a full rack of teeth had to be removed, and taken to the shop for repair.
3. A further problem with the rigid carrier teeth was that rocks of a certain size trapped in the flow patterns of the carrying zone became caught between teeth, providing a surface which carried shale and rocks past the discharge point and dropped it ahead of the disk. This is called forward spillage or carryover.
4. Compounding the forward spillage of shale is the tendency of the moist shale to compact on, and cling to the teeth. Loose shale "rides" on the clinging material, again spilling past the discharge point. Cold temperatures greatly aggravate the sticking material problem, increasing the forward spillage. Cleaning of the original carrier teeth to reduce carryover was not successful, because they were rigid, and many were always bent.